The invention relates to aqueous polyurethane dispersions, to a process for preparing them and to their use in cosmetic applications such as hair fixatives.
Polyurethane dispersions have recently been incorporated into cosmetic products, such as hair fixatives, suntan lotions, etc., offering several advantages over conventional technologies such as acrylics and acryl amide copolymers, polyvinyl pyrrolidone, and PVP/VA copolymers. Such advantages include water compatibility, ease of formulating low VOC sprays, water resistance and excellent film forming ability. Specifically in hair care products, polyurethane dispersions provide great setting effect without sticky feel, excellent style retention owing to the polymer's elastic memory, natural look and feel. All these attributes are highly valuable to the consumer. Commercial polyurethane dispersions designed as hair fixatives and hair styling polymers generally exhibit good high humidity curl retention, style retention, good feel and shine. However, their lack of adhesion to hair is demonstrated by extensive flakiness on hair after combing. This creates a significant aesthetic problem for consumers.
The challenge of designing a hair fixative polymer consists of achieving a balance between often conflicting requirements: the polymer should be hydrophobic enough to provide curl retention even under humid conditions, while it should remain sufficiently hydrophilic in order to be removable from hair by washing with water. Also, the polymer has to posses an optimum combination of glass transition temperature, flexibility and molecular weight to provide setting strength, elasticity, adhesion to hair and soft feel.
U.S. Pat. No. 5,626,840 discloses hair fixatives based on polyurethane dispersions that are prepared utilizing 2,2-hydroxymethyl-substituted carboxylic acid. It illustrates how to achieve good humidity resistance and spray characteristics using water soluble or dispersable polyurethanes. The examples demonstrate the efficacy of the polymer only in aerosol spray formulations containing alcohol. This is detrimental for both the environment and the health of the hair. Finally, the invention utilizes a range of dimethylol propionic acid (DMPA) of 0.35-2.25 meq of COOH per gram of polyurethane in the polyurethane dispersion that must be observed in order for the dispersion to be effective.
However, the disclosure does not teach how to avoid the common problem of the polymer's flakiness on hair by achieving good adhesion to hair. Moreover, it does not teach how to attain style retention, e.g. elastic behavior of the polymer. Finally, a lower amount of acid should preferably be used, while still achieving curl retention and washability, as the acid tends to accelerate the breakdown of the polymer.
U.S. Pat. No. 6,613,314 discloses reshapeable hair compositions that utilize polyurethane dispersions. During preparation of the polyurethane, an isocyanate-functional prepolymer is formed. The prepolymer incorporates at least one polyactive hydrogen compound that is soluble in the medium of dispersion. Preferably, sulfonated compounds are utilized. The sulfonic group is incorporated into the prepolymer, rather than via the urea segment.
U.S. Pat. No. 6,106,813 discloses polyester polyurethanes that are suitable in cosmetic applications. It discloses a new family of polyester polyurethanes that possess not only good film-forming properties, but also impart great rigidity and excellent resistance to removal by water and detergents. With regard to the hair styling/hair fixative applications, the examples in the patent demonstrate the use of the invention only in hair style shaping lotions, claiming good shape retention.
However, the reference does not mention adhesion to hair or how to achieve excellent humidity resistance with good removability by water. It also does not mention important attributes of hair styling/hair fixative polymers, such as natural feel and luster on hair.
Thus, the purpose of present invention was to provide a polymer composition which would improve adhesion to hair and also demonstrate excellent curl and style retention, natural feel and look.
The present invention provides a composition that demonstrates excellent adhesion to hair. In comparison to commercially available hair fixative polyurethane dispersions, the composition of the present invention impart significantly less or no flaking at all. In addition, it provides improved humidity retention, higher luster and natural feel in comparison to the above-mentioned polyurethane dispersions.